Astronomy Blog

Aurora from above

The northern or southern lights are a beautiful sight to see. Here is a lovely picture of the Aurora Australis (southern lights) seen from a rather unusual angle; looking down. The image was taken on 30th May 2005 from the International Space Station whilst it was passing over the Bass Strait in the southern Pacific. You can even see some star trails through it!

The aurora are caused when charged particles from the Sun hit oxygen and nitrogen atoms in the Earth's atmosphere and cause them to emit light. There tends to be more nitrogen than oxygen lower down in the thermosphere (say lower than 150km) and so colours due to nitrogen (red, blue and violet) tend to originate from there. The common green colour of aurora (and the only one I've seen) is due to oxygen atoms and occurs from altitudes between 100km and 300km. The less common red oxygen colour occurs at much higher altitudes - 300km to 500km - because the nitrogen density needs to be low for that type of emission to occur.

The crew of the International Space Station have taken many wonderful images of the aurora from their vantage point at about 370km altitude. Sometimes the crew have even found themselves in the "dimly glowing fog of red". Although that is an awe inspiring experience, there must be a bit of a worry about being amongst all those high-energy particles from the Sun.